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A novel 3D paper-based microfluidic screen-printed electrode (SPE) composed of two layers was constructed by photolithography and screen-printing technology. Aldehyde functionalized hydrophilic zone of the counter and reference electrodes layer was prepared for glucose oxidase immobilization. Highly conductive prussian blue deposited reduced graphene oxide-tetraethylene pentamine (rGO-TEPA/PB) modified paper working electrode layer can be used as an electrochemical sensitive membrane for quantitative detection of hydrogen peroxide (H 2 O 2), which was the enzyme-catalyzed reaction product. Therefore, this 3D paper-based microfluidic electrochemical biosensor can be used for quantitative detection of glucose. Under optimum conditions, the proposed biosensor can be used for quantitative determination of glucose over a wide linear range of 0.1 mM–25 mM with detection limit of 25 μM. Finally, the 3D paper-based microfluidic electrochemical biosensor was applied to determine glucose in human sweat and blood, and the obtained results were in good consistency with values measured by Roche's blood glucose meter. In addition, the proposed 3D paper-based electrochemical device showed good repeatability, stability, and anti-interference, which would be of great potential to monitor glucose in complex biological fluids. A novel 3D paper-based microfluidic screen-printed electrode composed of two layers was constructed by photolithography and screen printing technology. Aldehyde functionalized hydrophilic zone of the counter and reference electrodes layer was prepared for glucose oxidase immobilization. Highly conductive Prussian blue deposited reduced graphene oxide-tetraethylene pentamine modified paper working electrode layer can be used as an electrochemical sensitive membrane for quantitative detection of H 2 O 2 , which was the enzyme-catalyzed reaction product. Therefore, this 3D paper-based microfluidic electrochemical biosensor can be used for quantitative detection of glucose. Under optimum conditions, the proposed biosensor can be used for quantitative determination of glucose over a wide linear range of 0.1 mM–25 mM with detection limit of 25 μM. Image 1 • A paper based electrochemical approach for the determination of glucose is presented. • Enhanced stability, good selectivity, outstanding simplicity and low-cost biosensor. • Validation with the determination of glucose in human sweat and blood shows very good results. [ABSTRACT FROM AUTHOR]

Highlights • Au nanocomposites with ferrocenoyl cysteine conjugates were reported for fabrication of hemoglobin biosensor. • Biosensor showed very good performance at hemoglobin catalysis. • The proposed biosensor showed an extended linear range and lower detection limits. • The developed biosensor had an excellent efficacy for hemoglobin detection in the real samples. Abstract The abnormal content of hemoglobin in human body can lead to several diseases such as anemia, thalassemia, leukemia, heart disease. Therefore, it is very important for sensitive detection of hemoglobin in clinical analysis. An electrochemical approach is presented for detecting hemoglobin using disposable electrochemical sensors, which were based on the ability of the redox active ferrocene group of Fc[CO-Cys(Trt)-OMe] 2 and Fc[CO-Glu-Cys-Gly-OH]. The two electroactive materials were adsorbed onto gold nanoparticles that were previously electrochemically deposited onto screen-printed electrodes. The as-prepared sensors were characterized by scanning electron microscopy and energy dispersive spectroscopy, and their electrochemical properties were characterized by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. Results indicated the Fc[CO-Glu-Cys-Gly-OH] prepared sensor showed enhanced current responses for hemoglobin catalysis than the Fc[CO-Cys(Trt)-OMe] 2 prepared sensor. Optimal operating conditions were determined for hemoglobin detection by differential pulse voltammetry. The concentration of hemoglobin showed a good linear relationship with the current difference in the range of 0.1–1000 μg/mL and with 0.03 μg/mL limit of detection. The development of this electrochemical sensor was used for hemoglobin detection in human serum with a R.S.D. lower than 4.7% and recovery between 95.5% and 103.2%, which was in agreement with the data obtained from typical clinical analysis. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation method was adopted to investigate the absorption behavior, inhibition mechanisms on Fe (1 0 0) surface in aqueous solution and the diffusion behavior of H 3 O + , Cl − and H 2 O in three of 3,5-dibromo salicylaldehyde Schiff base inhibitor films, including 3,5-dibromo salicylaldehyde-2-pyridinecarboxylic acid hydrazide (L1), 3,5-dibromo salicylaldehyde-2-thiol-phenecarboxylic acid hydrazide (L2), 3,5-dibromo salicylaldehyde-2-aminobenzothiazole (L3). The effects of the interaction energy, radial distribution function and the self-diffusion coefficient were studied accompanying with density functional theory (DFT) study. The results demonstrated that the order of adsorption energy is E (L2) > E (L1) > E (L3), absorption manner is a multi-center chemical adsorption for three inhibitor films; for different inhibitor films, the diffusion coefficients followed the order of D (L3) > D (L1) > D (L2) for the Cl − corrosive particles, the diffusion coefficients followed the order of D (L3) > D (L1) > D (L2) for the H 3 O + corrosive particles. For the three inhibitor films, the diffusion coefficients of the three corrosive particles all followed the order of D (H 2 O) > D (H 3 O + ) > D (Cl − ). The inhibition efficiency order was obtained from the diffusion coefficient which is agreed well with the experimental results as EI (L2) > EI (L1) > EI (L3). Three kinds of inhibitor films have good corrosion inhibition efficiency in aqueous solution. [ABSTRACT FROM AUTHOR]

• The modified GE electrode enables target detection at a low optimal operating voltage of 0.2 V. • Layered electrodeposition of Zn-MOF and MWCNT on bare GE. • Zn-MOF and MWCNT increase electrode surface area and have better electrochemical detection performance. • The modified GE can be used for actual sample detection. A non-enzymatic glucose sensor was successfully prepared by the electrodeposition methods assembling of Zn-metal-organic frameworks/multi-walled carbon nanotubes (Zn-MOF/MWCNTs) on gold electrode (GE). The sensor showed better catalytic oxidation performance for glucose at very low potential (0.20 V) compared to the bare GE (0.30 V), because the modified complex can effectively increase the active site and reaction contact area. The sensor exhibited a wider linear detection range of 0.020–8.14 mM with a detection limit of 0.037 mΜ. In addition, the electrochemical response of the sensor to glucose showed good selectivity, which was further verified in the complex serum environment by the standard addition recovery method. The recovery of the sensor was in the range of 98.52–102.65%, with a relative standard deviation (RSD) of no more than 8.00%, showing the potential applications in real testing. [ABSTRACT FROM AUTHOR]

• A facile biotin sensor was fabricated based on heme conjugated with gold nanoparticles in situ at a glass carbon electrode. • The sensor heme/AuNPs/GCE can be applied for ultrasensitive determination of biotin with a wide range and a very low detection limit. • The sensor exhibited excellent selectivity, repeatability, reproducibility and stability, indicating high robustness. • The sensor was practical for accurately detecting biotin in various foods with easy homogenization and centrifugation. • We have made a clearer understanding of the electrochemical mechanisms of biotin. We report the fabrication of a facile sensor using heme conjugated with gold nanoparticles (AuNPs) in situ on a glass carbon electrode (GCE) for the ultrasensitive determination of biotin without antibody or streptavidin. The use of heme and AuNPs as dual amplifiers allows a very broad detection range from 0.0050 to 50.0000 μmol·L−1 and a very low detection limit of 0.0016 μmol·L−1. The mechanistic aspects were elucidated using electrochemical analyses and frontier orbital calculations showing that the electrooxidation of biotin involves a one-electron and a one-proton transfer, generating biotin sulfoxide. The heme/AuNPs/GCE sensor exhibited excellent selectivity, reproducibility and stability, indicating high robustness. The recovery was between 97.20 and 105.70% with RSD less than 8.71%, suggesting good practicability. Our studies demonstrate that this approach can be used to detect and quantify biotin in a range of foods, including milk, infant formula, flour, orange juice, mango juice, egg white and egg yolk. Furthermore, all measurements do not require any intricate preparation or pre-treatment of the foods, thus representing a great potential for point-of-care testing. [ABSTRACT FROM AUTHOR]

Sisal is a perennial tropical biomass with largest dosage in industry. Due to the special hard structure of sisal fiber, it can be prepared as carbon material and applied for negative material of lead-carbon battery. The pretreatment of sisal fiber was carried out by 5% NaOH and 5% H 3 PO 4 and tested by the measurement of FTIR, thermogravimetric analysis and SEM. Carbazole was doped in pretreated sisal fiber to prepare carbon material by a simple approach with two-step method. The characterization of the synthesis doped-N carbon material was tested by Raman, BET, XRD and EDS. According to the result of BET, it was turned out that the doped-N carbon material had a larger specific surface area. And the electrochemical properties were measured by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Besides, the cycling life test and charge/discharge curve were performed on battery testing instrument. In addition, the lead-carbon battery contained doped-N carbon material had a longer discharge plateau and a higher ultimate capacity. It was concluded that doped-N carbon material had a better electrochemical performance compared to undoped-N carbon material. [ABSTRACT FROM AUTHOR]

A novel fluorescence probe for determination of superoxide anion radical (O 2 − ) was developed with CdTe quantum dots(QDs) modified by thiophene-2-formaldehyde shrinked l -cysteine Schiff base, which was characterized by Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA), ultraviolet-visible (UV–vis) and fluorescent spectrum. The particle size of CdTe QDs was 3.1 nm as confirmed by X-ray powder diffraction pattern (XRD) and Transmission Electron Microscope (TEM) in presence of β -cysteamine (CA). The fluorescent results showed that the fluorescence intensity of CdTe QDs was decreased with modified Schiff base at 305 nm, but enhanced at 610 nm with O 2 − and showed an apparent linear dependence in the concentration scope of 2.0 × 10 −5 –1.0 × 10 −4 mol L −1 ( r = 0.9934) with a detection limit of 1.8 × 10 −6 mol L −1 , which exhibited high selectivity and stability towards O 2 − . [ABSTRACT FROM AUTHOR]

• A facile electrochemical sensor was designed for MEL detection. • The sensor was prepared by directly deposition of electroactive materials Fc-ECG on SPCE based on that MEL can enhance the electrochemical signal of Fc-ECG. • The sensor was used for MEL detection in milk samples. • A portable detection system with potential application in POCT was constructed. Excessive intake of melamine (MEL) can be harmful to human health, and it is important to establish a rapid and accurate MEL detection method. As the electrochemical activity of MEL is very low, ferrocenylglutathione (Fc-ECG) was used as an electron transfer mediator to assist with the detection of MEL using screen-printed carbon electrode (SPCE). This modified electrode (MEL/Fc-ECG/SPCE) was prepared by stepwise drop-casting and was fully characterized. Results showed that MEL significantly enhanced signal of Fc-ECG/SPCE sensor due to the three p-π conjugated double bonds that facilitated electron transfer. Under optimal conditions, the sensor exhibits two linearities in the range of 0.20–2.00 μM and 8.00–800 μM, with a sensitivity of 15.03 μA·μM−1·cm−2. The selectivity, stability, and reproducibility were investigated and successfully used to detect MEL in raw milk and confirms safety verification of foods. Moreover, a portable testing platform was designed for MEL detection based on a CH32 chip. [ABSTRACT FROM AUTHOR]